There are a number of polymers which are referred to as biodegradable polymers. Until quite recently these polymers have been used in high value add applications such as the medical and/or pharmaceutical field. Polymers such as polylactic acid or polylactides, polyhydroxybutyrate (PHB) and copolymers of hydroxy butyrate and valerate (PHBV) have been used to make articles such as absorbable sutures, osteo pins and screws, and in the field of controlled release drugs.
These types of polymers will "biodegrade" within a relatively short period of time, for example from about 6 to 12 weeks depending on the molecular weight and the polymer stereo chemistry.
There are some patents which disclose the use of such polymers in applications which are typically met by commodity polymers. These applications include for example films such as disclosed in Chemical Abstracts 95:63389r of Japanese Kokai JP 56/22324 which discloses a biodegradable mulch film; Chemical Abstracts 84:135650d and 84:18707e of U.S. Pat. Nos. 3,932,319 and 3,867,324 both assigned to Union Carbide which disclose films and molded plant holders of biodegradable polymers. Additionally, there is some art relating to films used in food packaging such as disclosed in Chemical Abstracts 110:153035e of European Patent Application 273 069 which discloses films of glacomannan as a food packaging and Chemical Abstracts 93:225641e of WO 80/659 which disclose latices of ethyl cellulose as a food coating. None of this art suggests a foamed degradable polymer.
The above art does not disclose that such polymers could be foamed. However, there is a need for degradable foamed polymeric products. Such products could be formed into trays for packaging cold products such as meat trays, or insulators for cold drinks, or for higher temperature applications such as containers for hot foods such as hot drinks or "fast food" such as hamburgers and the like (e.g. foamed trays and/or "clam shells").
Unfortunately the above type of packaging may be discarded by insensitive individuals causing unsightly waste. If such containers could be made from a polymer or polymer alloy which was degradable the problem of litter would be lessened.
Accordingly, there is a need for a degradable foamed polymeric composition. The present invention seeks to provide such a composition.